CODEWITHSUNDEEP
arraysmatlab
user2126062
user2126062

Reputation: 111

check if ALL elements of a vector are in another vector

I need to loop through coloumn 1 of a matrix and return (i) when I have come across ALL of the elements of another vector which i can predefine.

check_vector = [1:43] %% I dont actually need to predefine this - i know I am looking for the numbers 1 to 43.

matrix_a coloumn 1 (which is the only coloumn i am interested in looks like this for example

1 4 3 5 6 7 8 9 10 11 12 13 14 16 15 18 17 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 1 3 4 2 6 7 8

We want to loop through matrix_a and return the value of (i) when we have hit all of the numbers in the range 1 to 43. In the above example we are looking for all the numbers from 1 to 43 and the iteration will end round about position 47 in matrix_a because it is at this point that we hit number '2' which is the last number to complete all numbers in the sequence 1 to 43. It doesnt matter if we hit several of one number on the way, we count all those - we just want to know when we have reached all the numbers from the check vector or in this example in the sequence 1 to 43.

Ive tried something like:

completed = []
for i = 1:43
  complete(i) = find(matrix_a(:,1) == i,1,'first')
end

but not working.

Upvotes: 2

Views: 171

Answers (4)

Cornelius Sicker
Cornelius Sicker

Reputation: 160

Here is one solution without a loop and without any conditions on the vectors to be compared. Given two vectors a and b, this code will find the smallest index idx where a(1:idx) contains all elements of b. idx will be 0 when b is not contained in a.

a = [ 1 4 3 5 6 7 8 9 10 11 12 13 14 16 15 18 17 19 20 21 22 23 24 25 26 ...
    27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 1 3 4 2 6 7 8 50];
b = 1:43;

[~, Loca] = ismember(b,a);
idx = max(Loca) * all(Loca);

Some details:

  • ismember(b,a) checks if all elements of b can be found in a and the output Loca lists the indices of these elements within a. The index will be 0, if the element cannot be found in a.
  • idx = max(Loca) then is the highest index in this list of indices, so the smallest one where all elements of b are found within a(1:idx).
  • all(Loca) finally checks if all indices in Loca are nonzero, i.e. if all elements of b have been found in a.

Upvotes: 0

Luis Mendo
Luis Mendo

Reputation: 112659

To find the first entry at which all unique values of matrix_a have already appeared (that is, if check_vector consists of all unique values of matrix_a): the unique function almost gives the answer:

[~, ind] = unique(matrix_a, 'first');
result = max(ind);

Upvotes: 1

Divakar
Divakar

Reputation: 221514

Assuming A as the input column vector, two approaches could be suggested here.

Approach #1

With arrayfun -

check_vector = [1:43]
idx = find(arrayfun(@(n) all(ismember(check_vector,A(1:n))),1:numel(A)),1)+1

gives -

idx =
    47

Approach #2

With customary bsxfun -

check_vector = [1:43]
idx = find(all(cumsum(bsxfun(@eq,A(:),check_vector),1)~=0,2),1)+1

Upvotes: 2

matlabgui
matlabgui

Reputation: 5672

Someone might have a more compact answer but is this what your after?

maxIndex = 0;
for ii=1:length(a)
  [f,index] = ismember(ii,a);
  maxIndex=max(maxIndex,max(index));
end
maxIndex

Upvotes: 0

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